The Slingbox SOLO should work on a Windows 8 PC without an issue. Are you using a browser or the Classic Desktop Player? If you are using a browser, which one? I have placed a browser compatibility article below as well as an article walking through the steps of uninstalling and reinstalling the web plugin, just in case:
- Slingbox.com - What browsers are supported by Watch on Slingbox.com?
- Slingbox.com - Installing/removing browser plug-in for Watch on Slingbox.com
If you like, you can also try the Desktop Player by downloading and installing this from here:
I hope this helps!!